About the meaning:
The Book's meanings are mostly pretty straightforward, revolving around knowledge and education. There is at least one aspect though where different readers' opinions seem to divert. Some include "secret" in the Book's meanings, others don't. I write a bit more about that in the last paragraph.
Facts / truth / knowledge: First and foremost, the Book stands for knowledge, for facts, for the truth. It can represent anything which is factual, which corresponds with reality. It can indicate where the truth lies, or that the truth is being spoken or should be spoken. And because a book can be open or closed, the card Book can represent facts we are aware of, or facts that we don't (yet) know.
Learning / education / academics:
Closely related to knowledge is the process of acquiring it. In many readings, the Book very simply means that we have something to learn concerning a specific issue, that we need to acquire knowledge about a certain topic. If we're a student it can mean that it's time to pull ourselves together and put some study time in. Especially next to Child or Dog the Book could represent a person who is in the process of learning something, who is a student; next to the Bear, someone who is knowledgeable, a teacher. Sometimes the Book can also be a hint that it might be time for us to broaden our horizons by entering advanced training, or by enrolling in college. The Book can stand for any ongoing education, and academic endeavours. For example, especially in combination with the Snake, it can stand for an academic career or academic ambition. In combination with the Tower the Book may represent educational institutions, and in combination with the Bear, people with an academic and/or teaching profession.
Intelligence / intellect / intellectualism: Many readers interpret the book as intelligence, and I do, too. But I limit the intelligence the Book represents to intelligence in the sense of knowledgeableness, erudition, book learning - not practical, social, or emotional intelligence. In other words, for me the Book stands only for such intelligence as can be gained through good, theoretical education. So while the Book might say that someone is very well-educated, in possession of many facts, it does not say that this person also knows what to do with their knowledge. For example, knowing in theory what makes it possible to balance on a bicycle does not enable one to actually do it. And intellectually understanding power dynamics won't automatically make one a good leader. Also, the Book can stand for the intellect itself, and for intellectualism - for looking down on lifestyles or jobs that are more physical or creative. In some cases, the Book may mean that we are neglecting our physical and emotional health by focusing too much on our intellectual pursuits.
Categorisation / classification / filing: A very important part of the learning process is the sorting of new bits of knowledge, or separate individual facts, into pre-existing, superordinate, categories. This is the point at which we usually feel that we have understood a new piece of information: when we have found the class it (seems to) belong in. So to me the Book also stands for categorisations and classifications - both in a good sense (we've picked the appropriate category, so now we can use our new knowledge in an appropriate, productive way) and in the negative sense (inappropriate or even harmful stereotyped thinking, pigeonholing, an inability to think outside the box). In a rather neutral sense the Book just means that we are filing something or should file something (and then file it away).
Esoteric ("secret") knowledge: Traditionally, according to some, the Book is also interpreted as "a secret". I personally don't use this meaning - not in the traditional sense. One reason for this is that while, yes, if you haven't yet read a book what is written on its pages is not known to you. But it is right there, ready for you to discover it. You just need to pick it up and read it. It's not trying to hide anything! I find much more designed secretiveness in the Clouds or in the Mice. However, I do sometimes interpret the Book as esoteric knowledge. "Esoteric" knowledge is knowledge which is preserved only for a certain, intimate group of people; which is kept inaccessible or at least hard to access for the majority. In this esoteric sense, the Book does represent secrets to me, too.
About the Image:
Since good education means reading a lot of books, and since knowledge often does not just consist of one fact but of a conglomeration of many, I painted not just one book but a whole library. Also, a library symbolises very aptly that gaining knowledge can be a lengthy business. In a library, looking for knowledge, you might have to look through several books, follow new and unexpected leads, climb ladders to reach up to the higher shelves etc. In addition, private libraries used to be a source of pride. People liked to show off how educated they were by showing off their collection of books. So a library also is a great symbol for intellectualism. In my picture, there's an open book on the table to symbolise knowledge we have. But there are also many books yet closed to symbolise knowledge we don't yet have. Some libraries have bookshelves that also serve as hidden doors - you can swing them open and this will reveal either a secret little room or a staircase. There is such a door in my picture, too. The bookshelf is swung open, and behind it there are more books and a staircase leading upwards. These could symbolise "esoteric knowledge" dimension of the Book's meaning as well as the fact that educating yourself, gaining knowledge, is a never ending process. Every fact you learn is just a stepping stone that leads to yet another fact.
